Liquid crystalline materials are utilized in a variety of electrooptical and display device applications, in particular those which require compact, energy efficient, voltage-controlled light valves such as calculator displays.
Illustrative of organic materials which exhibit liquid crystalline behavior are (1) relatively stiff elongated molecules such as 4,4'-azoxyanisole; (2) polymers which are wholly aromatic in structure such as a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; and polymers with a flexible main chain and with side chains which exhibit mesogenic properties.
Low molecular weight liquid crystalline compounds exhibit optical properties while in the liquid mesogenic phase. Liquid crystalline polymers exhibit a thermotropic mesophase, and have the additional advantage that the optical properties can be preserved in the solid state.
As a further embodiment, liquid crystalline compounds have been incorporated as minute droplets in a porous polymeric matrix to protect the reactive material from atmospheric conditions and to enhance electric field behavior. Polymeric encapsulated liquid crystalline materials are described in U.S. Pat. Nos. 3,600,060; 4,048,358; and 4,579,423.
While the encapsulation of a liquid crystalline material in a polymeric matrix has desirable advantages, there are disadvantages associated with this type of composite structure. The polymer tends to cause spectral shifts of both absorption and emission wavelengths, and it can affect the photostability of the liquid crystalline material, and typically the polymeric matrix does not have a broad range of optical transparency.
Of background interest with respect to the present invention is Japanese Patent 73JP-098101 which describes a thermal type liquid crystal display device which consists of (1) a porous glass structure prepared by heating borosilicate glass to cause separation of phases, and leaching the boron oxide-rich and sodium oxide-rich phase with sulfuric acid to form a silica-rich porous glass; (2) a liquid crystal material in the pore volume; (3) a heating element coated on the porous glass in a pattern; and (4) a transparent protective cover.
Other publications of interest which describe the production of inorganic-organic composites are J. Phys. Chem., 88, 5956 (1984) and J. Non-Cryst. Solids, 74, 395 (1985) by D. Avnir et al, and Mat. Res. Soc. Symp. Proc., 73, 809 (1986) by Pope et al; incorporated herein by reference.
There is continuing interest in the development of improved liquid crystalline materials and structures which exhibit exceptional properties for specialized applications.
Accordingly, it is an object of this invention to provide novel liquid crystalline composites.
It is another object of this invention to provide a transparent optical medium which is a solid composite of a homogeneous porous inorganic oxide glass and a liquid crystalline component with enhanced photostability.
It is another object of this invention to provide a process for producing novel liquid crystalline composites.
It is a further object of this invention to provide optical devices which contain a novel liquid crystalline composite optical component.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
The subject matter of this patent application is related to that disclosed in copending patent application Ser. No. 15,759, filed April 17, 1987, and copending patent application Ser. No. 15,758, filed April 10, 1987.